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Agenesis of the Corpus Callosum

KEY POINTS

The corpus callosum is a major pathway connecting the two hemispheres of the brain. By the 17th week of gestation, the mature corpus callosum is formed.

In agenesis of the corpus callosum (ACC), the commissural fibers do not cross the midline but rather form thick bundles of fibers called Probst bundles, which course in a posterior direction along the medial walls of the lateral ventricles. These bundles indent and separate the anterior horns of the lateral ventricles.

ACC may be isolated, but often is associated with other malformations and genetic syndromes.

ACC occurs in <1% of the general population and in 2% to 3% of the developmentally disabled population.

The finding of mild ventriculomegaly during routine prenatal ultrasound examination should prompt a targeted search to confirm the presence of the corpus callosum.

The most consistent and easy-to-identify finding is the teardrop configuration of the lateral ventricles.

Prenatal magnetic resonance imaging (MRI) and three-dimensional ultrasound examination may be helpful in confirming the diagnosis. MRI may also be useful in identifying other subtle brain abnormalities that may not be apparent on sonogram but may have an impact on the long-term prognosis.

The natural history of antenatally detected ACC is not known due to the fact that there have been relatively few case series reported.

Fetal karyotype should be considered when ACC is diagnosed antenatally due to its association with chromosomal abnormalities.

Patients prenatally diagnosed with ACC can be managed according to routine prenatal care guidelines.

The neonate with suspected ACC should be examined carefully. MRI is the radiologic examination of choice.

ACC in addition to other abnormalities is often associated with poor neurologic outcomes. The long-term outcome of isolated ACC has not yet been elucidated.

CONDITION

The corpus callosum is a major pathway connecting the two hemispheres of the brain. The development of the corpus callosum begins during the 5th week of fetal life with the formation of the primitive lamina terminalis, which thickens to form the commissural plate. Glial cells coalesce to form a bridge-like structure that serves as a guide for the callosal fibers crossing the longitudinal cerebral fissure to their targets on the contralateral side of the brain (Rakic and Yakovlev, 1968). The mature corpus callosum is formed by the 17th week of gestation. In agenesis of the corpus callosum (ACC), the commissural fibers do not cross the midline; instead they form thick bundles of fibers, called “Probst bundles,” which course in a posterior direction along the medial walls of the lateral ventricles. These bundles indent and separate the anterior horns of the lateral ventricles.